In the seat belt device disclosed in following Patent Document 1, when a passenger applies a webbing to himself/herself, a buckle driving device is activated, and moves a buckle device toward a transverse direction outer side of the seat. Due thereto, the slack at the shoulder webbing, that restrains the chest portion and the shoulder portion of the passenger further toward the longitudinal direction proximal end side of the webbing than the tongue, is reduced.    Patent Document 1: Japanese Patent Application Laid-Open No. 2007-196881